House Speaker Nancy Pelosi said the president wants to "make America white again".

US President Donald Trump today assailed a group of Democratic congresswomen of colour as foreign-born troublemakers who should go back to the "broken and crime infested places from which they came". (AP)

Meantime Republican Rep Justin Amash of Michigan, a Trump critic who recently took steps to leave his party, called the remarks "racist and disgusting".

Mr Trump was almost certainly referring to Rep Alexandria Ocasio-Cortez of New York and her allies in what's become known as "the squad".

The others are Reps Ilhan Omar of Minnesota, Ayanna Pressley of Massachusetts and Rashida Tlaib of Michigan. Only Ms Omar, from Somalia, is foreign-born.

"So interesting to see 'Progressive' Democrat Congresswomen, who originally came from countries whose governments are a complete and total catastrophe, the worst, most corrupt and inept anywhere in the world (if they even have a functioning government at all), now loudly and viciously telling the people of the United States, the greatest and most powerful Nation on earth, how our government is to be run," he said in tweets.

"Why don't they go back and help fix the totally broken and crime infested places from which they came."

He added: "These places need your help badly, you can't leave fast enough. I'm sure that Nancy Pelosi would be very happy to quickly work out free travel arrangements!"

The others are Reps Ilhan Omar of Minnesota, Ayanna Pressley of Massachusetts and Rashida Tlaib of Michigan. Only Ms Omar, from Somalia, is foreign-born. (AP)

The attacks may have been meant to further the divides within the Democrat caucus, strained over internal debates on liberal policies and on whether to proceed with impeachment proceedings against Mr Trump.

What other Democrats said

Instead, Democrats as one voice denounced the comments, which evoked the old racist trope of telling a black person to go back to Africa.

"Unfortunately there is an American tradition of telling people to go back where they came from," New York City Mayor Bill de Blasio, a Democratic presidential contender, said on CNN's "State of the Union".

''It's a very bad tradition that we need to weed out of our nation because we are a nation of immigrants, that is who we are by our nature for hundreds of years.

“But you don't expect to hear it from the president."

It was far from the first time that Mr Trump has been accused of holding racist views.